Medical stents are tubular endoprostheses placed within the body to perform a function such as maintaining open a body lumen, for example, a passageway occluded by a tumor. Typically, the stent is delivered inside the body by a catheter that supports the stent in a compacted form as it is transported to the desired site. Upon reaching the site, the stent is expanded so that it engages the walls of the lumen. The expansion mechanism may involve forcing the stent to expand radially outward, for example, by inflation of a balloon carried by the catheter, to inelastically deform the stent and fix it at a predetermined expanded position in contact with the lumen wall. The expansion balloon can then be deflated and the catheter removed.
In another technique, the stent is formed of a highly elastic material that will self-expand after being compacted. During introduction into the body, the stent is restrained in the compacted condition. When the stent has been delivered to the desired site for implantation, the restraint is removed, allowing the stent to self-expand by its own internal elastic restoring force.
Strictures of the esophagus often produce obstructive dysphagia resulting in debilitating malnutrition. To date, the theoretical advantages of placing a plastic stent to restore the patient's ability to swallow have been offset by technical difficulty of placement, morbidity and mortality associated with the procedure, and poor long-term prosthesis performance. In particular, previous stents have transmitted the force and deformation of peristaltic waves inappropriately, for instance causing the stent to creep toward the stomach, perforate the esophagus, or rupture the aorta.